fix: scope transactional locks to primary records

backend/apps/tickets/draft_services.py

@@ -671,7 +671,7 @@ def _auto_create_ticket(
 
     # Agent/Celery 重试可能并发进入；锁定受理记录后再判断是否已经完成建单。
     draft = (
-        TicketDraft.objects.select_for_update()
+        TicketDraft.objects.select_for_update(of=("self",))
         .select_related("created_by", "confirmed_ticket")
         .prefetch_related("materials")
         .get(id=draft_id)
@@ -944,7 +944,7 @@ def cancel_draft_analysis(
     user,
 ) -> TicketDraft:
     draft = (
-        TicketDraft.objects.select_for_update()
+        TicketDraft.objects.select_for_update(of=("self",))
         .select_related("latest_agent_run", "created_by")
         .get(public_id=draft_public_id, created_by=user)
     )